1. Field of the Invention
The invention relates to a magnetic transducer and a thin film magnetic head using the same. More particularly, the invention relates to a magnetic transducer capable of obtaining resistance properties adaptable to ultra-high-density recording and a thin film magnetic head using the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk or the like. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive element (hereinafter referred to as an MR element) that is a type of magnetic transducer and a recording head having an inductive magnetic transducer, is widely used as the thin film magnetic head.
MR elements include an element using a magnetic film (an AMR film) exhibiting an anisotropic magnetoresistive effect (an AMR effect), and an element using a magnetic film (a GMR film) exhibiting a giant magnetoresistive effect (a GMR effect). The GMR film is mainly used in the MR element for the reproducing head whose surface recording density exceeds 3 Gbit/inch2. As the GMR film, a xe2x80x9cmultilayered type (antiferromagnetic type)xe2x80x9d film, an xe2x80x9cinductive ferromagnetic typexe2x80x9d film, a xe2x80x9cgranular typexe2x80x9d film, a xe2x80x9cspin valve typexe2x80x9d film and the like are proposed. Of these types of films, the spin valve type GMR film is used for the industrialization of a magnetic head.
The spin valve type GMR film has a stacked structure comprising a nonmagnetic layer; a magnetic layer having the fixed orientation of magnetization; and a magnetic layer having the orientation of magnetization changing in accordance with a signal magnetic field, in which the magnetic layers are stacked with the nonmagnetic layer in between. Electrical resistance changes in accordance with a relative angle between the orientations of magnetizations of the two magnetic layers. The spin valve type GMR film obtains the rate of resistance change of 2% to 6% (U.S. Pat. No. 5,408,377).
Moreover, a xe2x80x9ctunnel junction typexe2x80x9d GMR film utilizing a tunnel current passing through a thin insulating layer has been recently developed (U.S. Pat. No. 5,901,018). The tunnel junction type GMR film has a structure in which an insulating layer is sandwiched between two magnetic layers. During the passage of the tunnel current through the insulating layer, electrical resistance changes in accordance with the signal magnetic field. The tunnel junction type GMR film obtains higher electrical resistance as a junction area becomes smaller. However, shot noise is caused and thus the S/N (signal to noise) ratio becomes low. Therefore, the tunnel junction type GMR film has the limitations of improvement in properties of the magnetic head.
Therefore, attention has been recently paid to an MR element having the so-called CPP (Current Perpendicular to the Plane) structure in which a current is passed through the multilayered type GMR film in a direction of stacking (Japanese Unexamined Pat. Application Publication No. Hei 5-275769). The multilayered type GMR film has a stack comprising magnetic layers alternating with nonmagnetic layers. The orientations of magnetizations of the magnetic layers change in accordance with the signal magnetic field, and thus electrical resistance changes. The above-mentioned multilayered type GMR film is disclosed in, for example, Japanese Unexamined Pat. Application Publication No. Hei 4-360009, Japanese Patent No. 2610376, Japanese Unexamined Patent Application Publication No. Hei 5-90026, Japanese Unexamined Patent Application Publication No. Hei 7-78316 and Japanese Unexamined Patent Application Publication No. Hei 9-180135. According to the multilayered type GMR film, the rate of resistance change is about 1% to 10% when the current is passed perpendicularly to the direction of stack (Japanese Unexamined Patent Application Publication No. Hei 5-90026). The rate of resistance change is about 10% to 15% when the current is passed in the direction of stack.
However, currently, demand for high-density recording on the hard disk or the like is increasingly growing. Thus, the surface recording density exceeding 100 Gbit/inch2 is required. A size of the MR element must be about 0.1 xcexcm in order to meet the demand for such ultra-high-density recording. A higher rate of resistance change is needed in order to ensure high head output. Consequently, there is a problem that the heretofore-reported rate of resistance change of 10% to 15% of the CPP structure is insufficient.
In order to ensure high head output, it is necessary to increase resistance as well as the rate of resistance change. Although a conventional CPP structure can increase either the rate of resistance change or the resistance by selecting a material for constituting the magnetic layer, the conventional CPP structure has a problem of having difficulty in increasing both the rate of resistance change and the resistance. For example, when the magnetic layer is made of a material containing Ni (nickel) as the main ingredient, the resistance can be increased by adding an additive or the like, but the rate of resistance change decreases. When the magnetic layer is made of a material containing Co (cobalt) as the main ingredient, the rate of resistance change can be increased, but the resistance decreases.
It is an object of the invention to provide a magnetic transducer and a thin film magnetic head which have resistance properties adaptable to ultra-high-density recording.
A magnetic transducer of the invention comprises a stack having a plurality of magnetic layers alternating with a plurality of nonmagnetic layers. In the magnetic transducer, the stack has a plurality of regions into which the stack is divided in the direction of stacking, and at least two regions of the plurality of regions differ from each other in a material or composition of the magnetic layers.
In the magnetic transducer of the invention, at least two regions of the stack differ from each other in the material or composition of the magnetic layers. Therefore, both the rate of resistance change and resistance increase.
In the magnetic transducer of the invention, it is preferable that the stack has the region including the magnetic layers made of a material containing at least Ni in a group consisting of Ni (nickel), Co (cobalt), Fe (iron), Cr (chromium), Ta (tantalum), Rh (rhodium), Mo (molybdenum), Zr (zirconium) and Nb (niobium). Preferably, the stack has the region including the magnetic layers made of a material containing at least Co in a group consisting of Co, Fe and Ni. Preferably, the stack has a first region including the magnetic layers made of a material containing at least Ni in a group consisting of Ni, Co, Fe, Cr, Ta, Rh, Mo, Zr and Nb, and a second region including the magnetic layers made of a material containing at least Co in a group consisting of Co, Fe and Ni. Preferably, the first region has an end surface exposed to the outside for capturing a signal magnetic field.
Preferably, a thickness of each of the magnetic layers of the first region is from 1 nm to 6 nm inclusive and a thickness of each of the magnetic layers of the second region is from 1 nm to 4 nm inclusive. Preferably, the material or composition of the nonmagnetic layers included in the first region differs from the material or composition of the nonmagnetic layers included in the second region. Preferably, the number of the magnetic layers is from 2 to 20 inclusive. Preferably, at least one of the plurality of nonmagnetic layers is made of a material containing at least one element in a group consisting of Au (gold), Ag (silver), Cu (copper), Ru (ruthenium), Rh, Re (rhenium), Pt (platinum) and W (tungsten). Preferably, at least one of the plurality of nonmagnetic layers is made of a material containing Ni and Cr. More preferably, one of the plurality of nonmagnetic layers, which is located on one outermost side in the direction of stacking, is made of a material containing Ni and Cr.
Preferably, a thickness of the nonmagnetic layer is set so as to maximize antiferromagnetic coupling energy induced between two magnetic layers adjacent to each other with the nonmagnetic layer in between. Preferably, the antiferromagnetic coupling energy induced between two magnetic layers adjacent to each other with the nonmagnetic layer in between is from 0.1xc3x9710xe2x88x924 J/m2 to 2.0xc3x9710xe2x88x924 J/m2 inclusive.
A thin film magnetic head of the invention has the above-described magnetic transducer.
Preferably, the thin film magnetic head of the invention further comprises a current path for passing a current through the stack in the direction of stacking of the magnetic layers and the nonmagnetic layers. Preferably, the thin film magnetic head further comprises a pair of shield layers for sandwiching the magnetic transducer therebetween with a pair of gap layers in between, and the gap layers and the shield layers function as the current path.
Other and further objects, features and advantages of the invention will appear more fully from the following description.